Plural camera television control system



Sept. 22, 1953 w. L.. HURFORD PLURAL CAMERA TELEVISION CONTROL SYSTEM 4 Sheets-Sheet 1 Filed Oct. 24, 1950 H'ss Attorney.

Sept. 22, 1953 w. L. HURFQRDA 2,653,186

PLURAL CAMERA TELEVISION CONTROL SYSTEM i Filed om. 24, 195o 4 sheets-sheet 2 Figa.

Inventor: Winslow L.; Hurford,

His 'AttQPYwey Sept. 22, 1953 w. l.. HURFORD PLURAL CAMERA TELEVISION CONTROL SYSTEM 4 Sheets-Sheet 3 Filed 0G17.` 24, 1950 .DmPDO mv .MPP-202 .LOJLOO OBGIA Sept. 22, 1953 w. HURFORD PLURAL CAMERA TELEVISION CONTROL SYSTEM 4 Sheets-Sheet 4 Filed 00k. 24, 1950 Figlie.

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Patented Sept. 22, 1 953 PLURAL CAMERA TELEVISION CONTROL SYSTEM Winslow L. Hurford, North Syracuse, N. Y., assignor to General Electric Company, a corporation of New York Application October 24, 1950, Serial No. 191,873

2 Claims. 1

My invention relates, in general, to means for controlling the transmission of signals in an electrical system and relates, in particular, to means in a television system for changing in any desired manner the picture transmission from one subject, being televised by one camera, for instance, to another subject, being televised by another camera, for instance.

In the transmission of a television program it is common practice to use more than one source of television signals, for example, in a program of studio origin it is common practice to use more than one pick-up camera to televise the scenes and to switch from one camera to another during the presentation of the program. Abrupt changes from one scene to another are not particularly pleasing to the eye.

Accordingly one of the objects of my invention is to provide improved means for gradually replacing one video signal in a television system by another so that the effect produced upon the receiver screen is a gradual wiping of one scene off the screen while simultaneously unfolding another scene in a way which is pleasing to the eye.

Another object of my invention is to provide means for switching from one video signal to another at a high rate without introducing objectional switching or transient voltages which impair the performance of the television system.

An exemplary embodiment of the invention comprises a first amplier having an input circuit and an output circuit and a second amplifier having an input circuit and an output circuit. The input circuits are adapted to be connected, respectivelyy to first and second sources of video signal. The output circuits are adapted to feed a common utilization circuit. The amplifiers are alternately blocked by pulses obtained from a multivibrator type oscillator which is periodically triggered by the line synchronizing signal. The signal appearing in the utilization means is :a video signal made up of a combination of the first and second video signals. The portion of a particular video signal making up the combined video signal is determined by the width of the pulse from the multivibrator which in turn is controlled by a potential applied to thev multivibrator. By suitably varying the potential applied to the multivibrator, the portion of the particular input video signal in the combined video signal may be varied from substantially zero to a hundred per cent.

The nature of the control signal applied to the multivibrator and the manner in whichit is the television art.

varied determines the nature of the wipe effect produced. A simple wiping operation achieved by varying the potential applied to the multivibrator may be described as follows. Before the transition from one picture to the next, pulses from the multivibrator block out the second picture and allow the iirst picture to pass through. During the following frame since the control potential applied to the multivibrator has changed, the width of the pulse from the multivibrator has changed causing a small portion of each video line of the first picture to be blocked out and a corresponding portion of each video line of the second picture to take its place.

During following frames, the portion of each video line of the first picture which is blocked out is progressively increased until eventually the picture coming through the iirst amplifier is completely blocked out and the picture coming through the second amplier is allowed to pass. Thus, at any time during the wiping operation a combined video line is made up of complementary parts of video lines of the rst and second picture. By varying the potential applied to the multivibrator slowly, a slow wipe is produced. By varying the potential rapidly, a rapid wipe is produced. By applying special wave forms, as control potentials to the multivibrator, special wiping effects may be produced.

Accordingly, another object of my invention is to provide a simple circuit adapted to provide a Variety of complex wiping effects determined by the nature of the wave form applied to a control point of the aforementioned circuit.

A further object of my invention is to provide a means for automatically displacing one video signal by another so that as one scene is being wiped oi `the screen at the receiver another scene at the same time is taking its place.

In motion picture projection, various ways are employed for gradually changing from one scene to another. One of these methods is a wipe The present invention is particularly addressed to the production of various wiping effects in A wipe is the passing, at any desired velocity across a screen, of a contour of any desired shape, on one side of which one picture is presented and on the other side of which a second picture is presented.

A feature of the invention is the control of the contour motion and characteristics of the "wipe by electrical waveforms.

A further feature of my invention is to provide means for wiping a plurality of pictures onto and then oft ak television screen so that the effect appearing at the television receiver is that of one view displaced by ranother in any desired manner.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, Y-looth'as fto its organization and method of aoperato'n, `together with -further objects and advantages thereof may best be understood by reference to the .following description" taken in connection with the` accompanying synchronizing pulses .applied from an external .source to the multivibrator through an amplifier drawings in which Fig. 1 is ablock'diagr'am of circuits embodying my invention; Fig. 2 shows various waveforms that appear atvar'ious ,points in the circuit of Fig, 1; Fig. 3iislaischematicdiagram of the circuit shown in block form in Fig. 1; Figs. 4a and 4b and 4c illustrate vone of-thelpic ture effects that may be produced by my'invention; Fig. 5 is a diagram showing how theposi-Y tion of the wipe line in Fig. 4c may be varied are appliedf'to the/multivibrator 2l.

i3 fand a Tkey'er'Ladapted tto derive a pulse 'from the synchronizing signal corresponding to fthe `:trailing -edgeof the synchronizing pulses. Waveform fEslic'wsithe triggering pulses which The Width oi` theipulses obtained from the multivibrator 2i maybe varied by varying the control potential by fvaryingfthe voltegeeppliedftofafcontrolpoint.

` of-.an exemplary embodiment yfof, =my invention;

Fig, B -illustrates afvariety of efects that may be produced by applying suitable control voltage wayeiorms to, Athe AQontrol point of. venoxompa'ry embodiment Aoi my invention- 'Eheoperation ofvanzeiemplaryrembodiment of i i my invention Will best bev understood by first Considering 4the block 'diag-rompi Fig.. 1. in coni junction with the. WaveormfdiesromoiFig. 2.

foriesemple, trom-first. endgsecondfetuclio cameras teievisirie different scenes. .These yvideo signals i are applied to terminals -i andk respectively. i For the-purpose@ explanation@ the. invention,

ihersirideo'sieeeifeppliedet terminal i. Vis-iiiede anessentially -White scene while .the'seoond video signal `applied at terminal VZvis made an essentiallyVv blaci; scene.V flhe firstl and secondA video Y* 'Ehe iirst` -v-ideo signal 4iSv-applied' to a variableV gainyideo amplifiere in -Whicha oontrcl-isprof vided-for varyingftheigain of'the-ampliiier. 'Lho videosignal is next Tpas sedthrough another -video I amplier'whichlfunctionsfto isolate the source of video from thekeying Atransients in theinput 1 circuits associatadlwith vthe keyedvideo ample er L0. lEhe signalisl-neiit applied to the input channellthroug'h which -tlfieY second vided-signal applied'a't terminalfZpassesjis similarltotheirst v videol channel .and comprises a variable gain p videoamplier lil, aniisol'ation video amplier i5,"a'nd."a'kyed video amplifier i6, ,y

The fkeye'i video amplifiersV lo and i6 Which mayjbere'garded .'asflectronic switching means plied tothe Vv'cathode ciriiits'of .the keyed video amplifiers@ anais over consumers' sa am; me,`v respectively, are ci oppositeV polarity thereby per*-Y are"kyed hypilseslderiv'ed'from multivibrator 2l throughl keying ampliiiersl [8, and I9, and anVA V mittingnonly one video yarnpliiier to -pass or conduet elf-Signal et-onetime .-'lheoombiped video VYsignal appearing at the. output of. the keyed.

video amplifiers it analyte comprises afvideo sig,- nalma'de up offagportiono the 'fvideo signalifriom.

the-first video channel landzipart v.of theivideo.

` signalfrom'the second videosachannels Relative. 1

vapplied to terminal 3 I.

Ywaveform J.

`faotoryfpepiorinanceiirrsubsequent:circuits.; 13..

Accordingly, the edges 25 and 26 of keying waveforms F and G may be varied from @.Cgflit) 218 and "H0111 ieg; 9147.9 edge 3ii.,-respeotive1.y, -by.varyir1e-the ooptroipo.- tentialA yapplied kto terminal v137| 'in .order ato 'vary the portionpf-each videosignal appearingk in the` combined video signal-'at the-:output -offthekeyed;v video amplifiers inpandit.

-WaveformJ shows the outputs 'of `keyed videor amplifiers It and I6 which are applied to-video: v amplier rt3. Waveform shows vthel eontribuf tion oi keyedfamplier t0; to `the y coinbinedyideo signalshown as waveform J. Waveform .Ifshows. the-contributionof keyed amplierii to .the-come bined yideo outputsignal. With amplii'iers 4lilland l/in normal operation, the vvkeyed video Vamplier IB is on-duringrtheltimethat keyed video amplier itis on and-vice versa. Y n

Whenever the keyed video .ampliiiers fare'V switched .from alconductive to a'nonconductive` state or vice versa, 4spike-.shaped fvoltagepulses or ktransients are producedfin the output `circuit o1" the keyed -videoampliers Eiland it. These spike-shaped voltageh pulses 35 are shown TheA spiked-shaped -voltage.pulses. 35 'eXtendinto the.' black region. of. the. .video i s'ig. nal as shownin waveform `J. f

Inorder to facilitate removal ofthe spikedshaped voltage /puises '35 from 4thev'viiec. signaly appearing .at theoutputfofthe videov amplifier. 33, a'blankling signal' whichmay'be .either positive or negative is *applied4 through the 'bflanling oril pedestal .amplifier SB'V to. increase vthe `amount of blanking 'or `.pedestal appearing in the output video signal as shownat waveformfK. Theremoval of 'the spiked-shaped vltageplsesis'accornp'lishedfbyV a "circuit arrangement called a series-clipper. Theseries clipperfij'lremovesftlie portion io'ift'he waveform K shown above ".th'e` dotted line'tolproduce 'the Waveform Il 'The signal having wav'formL 'is'then'passedthrough a video" varnp'liner 733A and output' amplifiers f and .lill/to thefvidleojoutput fterrninal"i,v The terminal e l 4permitsi.ip'oipit'oririgoji the y'iiieooiltf.n put. "i i' In 'any .ii-+C.; apio iieroffthekipii involyed the 'apparatus .oi E 1;; thepesaee off. afvitie'o signal. therethrough 'I ects a reinovaljoij the.; D.'C. reference.levelfofthe Agio. signet. The'. video signal .inj passing throughvr video arriplii'ersVr losjesj its. direct""currentVreferenceievel, "for xample, .aniL-C.v signaljmay vbeV either apositive 1 or negative.signal:depending.onyvliich .partici L.the .e signalA is Ytaken as y zero reference'- level', Y. Accord;- ingly, n it is necessary Yto :supplygcircuits ;to :rein-in' serifthegi'eerenoe-lev ordertogl obtain;satis-Y C. rinsertion is achieved in the apparatus shown y in block form in Fig. 1 by means of circuits referred to as keyed clamps Il, I1 and 23.

The keyed clamps Il, l1 and 23 are diode circuits which effect a readjustment of potential appearing at the input to the respective ampliiiers I9, I6 and 33 at the end of each video line so that the signal appearing at the output of the video ampliers has the proper D.C. or unidirectional component. The keyed clamps Il, I'I and 23 are keyed at the end of each video line by the lkeyers I2 and 24, respectively. The keyers I2 and 24 render the keyed clamps Il, I1 and 23 operative at the end of each video line to permit readjustment of the aforementioned unidirectional component of signal potential. 'The clamped keyer I2 is timed or keyed by a synchronizing signal shown as waveform C supplied through synchronizing signal amplifier I3. The clamp keyer I2 differentiates the synchronizing signal to produce two pulses of opposite polarity corresponding to the leading and trailing edges of the synchronizing pulses of the synchronizing signal. The clamp keyer I2 also removes or clips the portion of the differentiated signal corresponding to the leading edges of the synchronizing signal and applies the resultant signal which appears as waveform E in Fig. 2 to one-half of the keyed clamp II. The clamp keyer I2 also supplies the signal of waveform E with reverse polarity to the other half of the key'ed clamp II.

The clamp keyer I2 also keys the keyed clamp I'I. The keyed clamp 23 and the clamp keyer 24 function like keyed clamps Il and I'I and clamp keyer I2 to reinsert the D.C. component of the video signal lost by passing the video signal through the keyed video amplifiers I and l5. The waveform applied from the clamp keyer 243 to one half of the keyed clamp 23 is shown as waveform D in Fig. 2. A similar waveform but of opposite polarity is applied from the clamp keyer 2d to the other half of the keyed clamp 23.

Referring now to Fig. 3, there is shown a schematic drawing of the circuit shown in the block diagram of Fig. 1. Video amplifiers 8 and S are conventional video amplifiers. Potentiometer d2 is a gain control for varying the video gain of amplifier 3. Preferably the amplifiers 8 and 9 are completely shielded from each other and other components in the circuit. Video ampliiers I4 and E5 are similar to video arnpliers 8 and 9 and likewise are preferably shielded. The output of video amplier 9 is supplied to the grid 43 of keyed video amplifier I9 which preferably comprises a pentode in which the screen grid 54 is voltage stabilized, for eX- ample, by voltage regulator device 22. The output of video amplier I5 is supplied to a second keyed video amplier I6 which also preferably comprises a pentode similarly having its screen grid 135 voltage stabilized. The plates of the keyed Video ampliiers I9 and I5 are connected together and to the B+ supply through the common plate load 45. Keying pulses are applied to cathode resistors 41 and 48 of the keyed amplifiers Iii and I5. The cathode 49 of keying ampliiier is is connected to the cathode 59 of the keyed video amplifier I9 over conductor 18a. The cathode 5I of keying amplier I9 is connected to the cathode 52 of keyed video ampli- Iier It over conductor I 9a. Whenever a positive pulse is applied across either cathode resistor 4i or cathode resistor 48, ther corresponding cathodes 4l' and 48 are driven positive with respect to the corresponding grids thereby rendering either amplier I0 or I6 nonconductive. The pulses applied to the grids of the keying amplifiers I8 and I9 are of reverse polartiy since the pulse applied to the grid 53 of keying amplifier I8 is obtained from the plate 54 of keying amplifier I9. The keying waveform applied to the grids 53 and 55 vof the keying ampliers I8 and I9 are obtained through an isolation ampliiier 29 from multivibrator 2| which comprises electron discharge devices 55, 57 and 58.

The multivibrator 2I is of the cathode coupled one-shot variety. The cathode follower stage 51 between electron discharge device 55 and 53 of the multivibrator 2| functions to decrease the switch overtime from one state of operation of the multivibrator to another. The width o the pulse obtained from the multivibrator 2| is determined jointly by the time constant comprising capacitor 59 and resistor 69 and by the unidirectional potential applied to the grid 6| of electron discharge device 5B. The parallel combination of resistance 62 and capacitor 63 and also the parallel combination of inductance 64 and resistance G5 functions to improve the waveform of the output of the multivibrator 2 I. Since the resistance 69 and capacitance 59 are fixed, the pulse width of the multivibrator 2| is determined by the potential applied to the grid 5| of the multivibrator 2l.

The multivibrator 2| is triggered by means of the triggering amplifier 56, the grid 67 of which is connected to a source of triggering potential. In the embodiment shown the triggering potential is a pulse derived from the trailing edge of the line synchronizing signal and is obtained from the clamp keyer I2. The plate or anode t8 of the triggering ampliiier 65 is connected to the plate 59 of electron discharge device 55. Application of a triggering pulse to the triggering amplifier 66 produces the potential drop in the plate circuit of device 56 and initiates the operation of the multivibrator 2|.

Brieny the operation of the multivibrator 2| is as follows: At the beginning of the cycle, since the grid lil of the electron discharge device 5c is connected to B+, the electron discharge device 533 is conducting heavily developing a high bias across cathode resistor ll. Since resistance il is common to devices 56 and 58 a large current through resistance II places cathode of device 55 at a high positive potential with respect to grid 5| thereby first electron discharge device 5S of the multivibrator 2l is maintained cut-off. When a pulse is applied to the triggering amplifier 68, it draws current through resistor l2 dropping the potential at the plate Si! of device 5E. This drop in potential is transmitted to the grid 'I3 of the cathode coupled amplifier 5l, since device 57 is connected as a cathode follower circuit av drop in grid potential causes a drop in the potential at the cathode lll. rIihe drop in potential at the cathode Id is transmitted through capacitor 59 to the grid 'it tending to drop the potential of grid 'i9 farther and render the device 58 less conductive, Dropping the potential of grid 'I9 of the electron discharge device 58 decreases the cathode bias of the devices 56 and 53 sufliciently so that now device 55 of the multivibrator is conducting and the device 58 of the multivibrator is .cut-off. As the capacitor 59 charges up to B+ potential, the device 5,8 eventually becomes conductive again and device 5B becomes nonconductive. The time during which device 56 estense tential setting on 4its grid 61 and by the time constant comprising capacitor -59 and resistance 69. vControl potentials vmay '-be applied vto the grid Sl through potentiometer yHi8 which forms i part of a voltage divideracross the B+ supply.

Movement -of the arm 109 of the potentiometer will cause the Width'of -the pulse, obtained from i the multivibrator to changein accordance therewith. The potentiometer# 08 may be disconnected from vthe multivibrator Yand potentials of various waveforms may be applied at point H to produce special wiping effects.

Circuits T and 'I6 are direct current restorer circuits,conventionaln fthe artand functioning to maintain the proper -D;C. reference level for the pulses from isolation amplifier 20 applied to theY grids "55 and '53 ofykeying amplifiers I9 Y and i9. Were ^it not for the D;C. restorer circuits l5 'and '16, the D.C. reference level Would-change asthe Width of the pulses applied to the grids 53 yand '55 changed. The proper D.C. restoration-of 'the video signal appearing at'the input of-amplifier''is 'achieved'by means ofa keyed clamp 23. Proper D.C. reinsertion at Ithe inputs of keyed video amplier IB and keyed Avideo amplier It is likewise achievedby means of keyed clamps Iii and yl'i respectively.

which act as switches to connect one side of each of capacitors iria, lic, and 23a, respectively, to the center tap on potentiometers it, 99 and toground, respectively, during a portion of the horizontallblanking interval. The operation of keyed clamps il and '23 Will be understood from ari-explanation of the operation of keyed clamp il.

` The keyed clamps Il, l1 and 23 are circuits During the aforementioned blanking interval p the accumulation of charge on capacitor lla develops acertain voltage bias across this capacitor depending on -the setting of the potentiometer it@ and on the amplitude of the blanking y signal. Duringf-the occurrence of the video Yline the .keyed clamp il presents an open circuit between "the aforementioned .side of capacitor Ila and the center tap of potentiometer lil input to the amplifier is .tied to or starts from a certain xed potentialV corresponding to the settingY of potentiometer |90 vthe D.C. component ofthe video signal assumes the proper value.

The manner of operation of the keyedV clamp Il to connect one side of capacitor liuto the center tap of potentiometer 99 for only a portion of the blanking interval will be apparent from the follovving'explanation. Negative pulses derived from lagging edges of line synchronizing signal are applied through capacitor 8G to the cathode of Idiode "I1 while positive pulses-derived from the lagging edge vof the line synchronizing signal are applied: throughY capacitor .88

to the .i plate of. ydiode 1.3. 18 ..are oppositely .'connected, the application. .of

Since diodes .11 .and y the aforementionedjpulses tofthev diodes jpera mits current to flow in either direction to capacitor HA from the center tap of potentiometer i90. Simultaneously with vthe application of *the aforementioned pulses to the diodes l1 and 18, a blanking voltage signal is applied across capacitor Ha from the output of amplifier 9. Thusa bias voltage is developed across capacitor Ila which is dependent on the voltage at the centrerwofpotentiometerV vlili) and on the amplitude of Vthe 'blanking signal. Upon the disappearance ofthe aforementioned pulses the diodes 'il' and i3 are rendered nonconductive by positive and lnegative voltages developed acrossjresistors lia and 18a. respectively, Vby the discharging of capacitors 89 and 38, respectively, whichV becarneY charged during `the application ofthe aforementioned pulses, Accordingly, the aforementioned bias voltage is retained at capacitor Hc during the occurrence of the video line. The operation of keyed clamps il and 23 is similar to the operation of keyed clamp il explained in the foregoing paragraphs.

The double diode clamps Il and Il are keyed or actuated in accordance with the above eX- planation by means of clamp keyer i2 Which'coinprises electrondischarge devices 8l and 32. Positive synchronizing pulses are applied Vto the grid 83 of an electron discharge device 8|. The output of device 9i is differentiated by capacitor 84 and resistor $5. The portions of the differentiated pulses corresponding to the trailing edges of the synchronizing pulses are amplified While the other portions of the differentiated pulses are clipped or removed by the amplifier-S2. The output from the plate oi amplifier 62 isV applied through coupling capacitors t6 and 8l to diodes 1'! and 79 and the output from the cathodes of amplifier -82 having an opposite polarity is applied through coupling capacitors 88 and S to diodes i8 and 89. Potentiometers 99 and it set .the D.C. reinsertion level.

The diode clamp 23 comprising diodes -99 and 9i are keyed by means ci clamp keyer 2li which is similar to clamp keyer i2. Al positive synchronizingsignal is applied through coupling capacitor 92 to the grid 93 of device 94 of the clamp keyer 24. The output of device 9d is differentiated by resistance 95 and capacitor 95. Theportion of the 'differentiated pulses corresponding -to the leading edge'of the synchronizing signal is ampliiied While the portion corresponding to Athe trailing-edge of thelsynchronizing signal is clipped so thata pulse signal of one polarity correspond- .ing to the leading edge of thef'synchronizing signals is Vapplied to one diode 99 through capacitor 91 While .a pulse signal of .opposite polarity is applied through coupling capacitor 98 to the other diode '9L 1 Y The clamp keyer 2s supplies pulses-to the'keyed clamp 23 which are derived from the leadingY edges of the synchronizing signal in order to avoid unproperireadjustment of the potential applied to the input of video amplifier .'39 due to `the* video,.ampliiier 3.3.- ivith...the consequent improper unidirectional component of signal at the output of video amplifier 33. Hence, in order to avoid clamping on the spike-shaped voltage pulses in the D.C. reinsertion process, the keyed clamp 33 is triggered from a pulse obtained from the leading edge of the synchronizing signal as shown in wavefrom C.

Thus, the keyed clamps Il, il and 23 effect a readjustment of the bias potential on the grida of the ampliiiers i0, l and 33 after every horizontal line during the blanking interval.

Further details as to the operation oi the i-C. reinsertion circuits which include the above referred to keyed clamps and clamped lreyers may be had by referring to U. S. Patent 2,299,9fi'- Wendt, and to U. S. Patent 2,313,906--Wendt, and to an article by K. R. Wendt appearing in the R. C. A. Review of March 1948.

The video signal from amplifiers I0 and i6 is applied to the grid mi of video amplier 33 which preferably comprises a pent-ode. The output signal appears across plate load impedance |02 comprising resistance |03 and inductance |04. The resistance E03 and inductance i @li is also the load impedance for the blanking or pedestal ampliiier towhich either a positive or a negative blanking signal may be applied. The addition of additional pedestal signal to the video signal appearing at the output of the ampliiier 33 is for the purpose of facilitating removal of the spikes introduced into the video signal by keying ampliers l0 and I6. The series clipper 31 including diode Elia and clipping level setter potentiometer it functions to clip ofi a portion of the black level of the video signal appearing at the output of the amplifier 3S in order to remove the spikes in the manner suggested by dotted line 3B in waveform K of Fig. 2. Since the negative side of rectier device Hita is connected to a source of BJ.- potential through potential divider |05, the lowest potential to which the plate H06 may drop and still maintain a current through device lii is limited and is determined by the setting of potential divider i05. The potential divider me controls the clipping level denoted by line 3e in waveform K. The output from the series clipper 3'! is then applied to ampliers 3S, 30 and 40, and appears at point '1.

Referring now to Figs. 4a, 4b and 4c there is shown the manner in which one scene is wiped off a receiver screen While another scene is wiped on the screen. Fig. 4c shows the manner in which the displacement of the scene of Fig. 4.a by the scene of Fig. 4b is achieved on the screen or" a television receiver. The line i0? in Fig. 4c is gradually caused to move across the composite lscene or picture from right to left until the scene -of Fig. 4a is completely wiped onc the screen while the scene of Fig. 4b takes its place. Movement of the line l0? is achieved by applying a control potential as shown in Fig. 5 to control grid 6I of the multivibrator 2i. By varying the control potential applied by potentiometer 03 to grid 6I the line |01 is made to move from right to left or vice versa.

Referring now to Fig. 6 there is shown schematically the manner in which other wiping effects may be achieved by the system described above. By applying the waveform shown in Fig. 6a to the control point 3l of the multivibrator 2 l, the wiping effect progressively shown in Figs. Gal, 6112 and 60.3 is obtained. Figs. Gal, 6012 and 6a?, represent successive elds in the transmitted television picture. The waveform of Fig. 6a has a repetition rate of 60 cycles per ,SecQnd correv l0 sponding to the number of fields per second. Potential corresponding to point II2 applied to the control point of the multivibrator represents a condition in which horizontal lines of scene B only appear on the screen. The potential corresponding to point I|3 represents a control potential during which horizontal lines of picture A alone appear on the screen. By varying the control potential periodically at a 60 cycle rate between these two points the progressive effect of wiping picture A 01T the screen and picture B on the screen is obtained. Fig. 6b and Fig. 6c show other waveforms which may be applied to the control point 3l to produce the progressive wiping eects shown by Figs. 6121, 6112, 6193 and Scl, Go2, crespectively.

The waveform of Fig. 6a may be produced from an ordinary electron discharge device triggered sweep circuit in which the grid bias of the sweep electron discharge device is progressively changed. The waveform of Fig. 6b may be produced by a full wave rectier and a clipper. As the magnitude of output Waveform from the rectier is progressively changed in magnitude, the waveform shown in Fig. 6a is produced. The waveform of Fig. 6c may be produced by a multivibrator operating at a 60 cycle rate and in which the pulse width is varied as shown.

While I have shown particular embodiments of my invention, it will of course be understood that I do not wish to be limited thereto since many modifications, both in the circuit arrangement and in the instrumentalities employed, may be made and I therefore contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. The combination, in a television system in which a plurality of images to be televised are scanned line by line, and in which said images are reproduced line by line on a remote screen, of a common transmission channel, a pair of individual channels each carrying signals varying in accordance with respective ones of said images, a pair of electron discharge amplifiers each having an output circuit connected to said common channel and each having an input circuit connected to respective ones of said individual channels, a multivibrator adapted to produce a single control pulse in response to synchronizing pulses applied thereto, means for applying synchronizing pulses synchronized with said line by line scanning to said multivibrator for developing control pulses synchronized with said line by line scanning, means for applying said pulses in one phase to one of said amplifiers and in the opposite phase to the other of said amplifiers whereby said ampliers are rendered alternately conductive at said line by line scanning rate, thereby line by line a portion of said one image and a complementary portion of said other image is produced on said remote screen, means in association with said multivibrator responsive to a unidirectional control potential for complementarily varying the duration of the control pulses applied to said amplifiers in accordance with the variations of said control potential, means for applying a unidirectional control potential varying in a predetermined manner to said control potential means to vary complementarily in a predetermined manner portions of said two images appearing simultaneously on said screen.

2AV The combination, in a television systemV in which a pairof images-to be televised arescanned dual channels each carrying signals varying in accord with respective ones' of said imagesa pair of electron discharge ampliiiers each having an output circuit connected to `said commonchannel and each having an input circuit connected to respective onesof said individual channels, each of said amplifiers including means responsive to a'voltage of predetermined magnitude and polarity applied thereto for renderingk said amplifiers nonccnductlve, a pair of electron discharge devices,A circuit means- Afor rendering each ofl said devices conductive whenV the-other is nonconductive, circuit means ior'rendering conductive that one of' said devices that isnonconductive whereby that device becomes conductive and the other device becomes nonconductive, circuit means for rendering said one ,deviceV nonconductivev again after Ya predetermined interval, said rsecond circuit means including means Vfor synchronizing the periods of conduction ofsaid one device with said line by linel scanning, means for deriving an output from one of said` devices having an amplitude exceeding said-predeterminedmagnitude,

to theV voltage responsive means of one of said ampliers and inv the opposite polarity to the voltage responsive means' of the other ofv said ampliers, whereby said' one amplier becomes nonconductive during the conduction of said one device While said other amplifier becomes nonconductive and said other amplifier becomes conductive during theconduction of said other de'- vice While the said one amplifier becomes nonconductive, thereby'line by line a portion of said one image and a complementary portion of said other image is produced on said remote screen.

WINSLOW L. HUB/FORD.

Referencesoitea, in the sie. of this patent UNITED sTATEs PATENTS Number Name Date 2,233,317 Konkle Feb.V 25, 1941 2,240,420 Schnitzer Apr. 29, 1941 2,244,239 Blumlein et al June 3, 1941 2,286,540 Hanson June 16, 1941 2,490,561 Ussler Dec. 6, 1949 2,546,338 Glassford Mar. 27, 1951 2,613,263 Hilburn Oct. 7, 1952 

